Carbon Stocks

Now that we understand what carbon is and why it is at the center of climate discussions, it's time to investigate where it is stored on the planet.

The answer is surprising: most of Earth's carbon is not in the atmosphere, nor in forests, nor in surface oceans. It is, in fact, in rocks.

99% of carbon is in rocks

That's right: about 99% of the planet's carbon is stored in sedimentary rocks, mainly limestone, composed of:

• Calcite (calcium carbonate – CaCO₃)

• Dolomite (calcium and magnesium carbonate – CaMg(CO₃)₂)

These rocks formed over millions of years from the combination of CO₂, water, minerals, and very slow geological processes. The atmospheric CO₂ was gradually transformed into carbonate and deposited as marine sediment, later compacted into solid rock.

In the geological map shown below, we can see large limestone formations spread across various continents. All of them are essentially ancient stocks of mineralized atmospheric carbon.

These stocks are smaller in volume but more dynamic and sensitive to human action. They are the ones we address when talking about carbon markets, reforestation, regenerative agriculture, among others.

Details of mobile stocks

These numbers help visualize the scale of the reservoirs. For example, there is more carbon in soils than in vegetation or the atmosphere — something few people know.

Ecossystems and their stocks

The distribution of carbon varies greatly according to the biome and type of soil. Some examples:

This differentiation is essential for land use planning, carbon credits, and conservation.

Static or dynamic?

Some stocks — such as rocks and deep sediments — are practically inert, beyond the reach of human action in the short term.

Others — like forests, agricultural soils, surface oceans — are highly dynamic, and therefore play a central role in climate mitigation strategies.

In the next post, we will dive into the dynamics of carbon: how it circulates among these stocks, naturally, in the planet's geological and biological cycle.